Many firearms typically include an ammunition magazine disposed somewhere within the frame of the firearm. Rounds of ammunition stored in the magazine are individually fed from the magazine into a barrel or firing chamber, where each round is fired. With a semi-automatic firearm, such as the Smith & Wesson model M&P 15 for example, the bolt, a mechanical part of the firearm that forms the rear of the chamber as the propellant burns, cycles back and forward between each shot, propelled by recoil or expanding gas (back) or the recoil spring (forward). When the bolt moves forward, it strips a cartridge from the magazine and pushes it into the chamber. When the bolt moves back, an extractor pulls the spent casing from the chamber. Once the case is clear of the chamber, the ejector ejects the casing out of the firearm so that a new round may be chambered.
After the firing of the last round in the magazine, a “bolt stop,” also known as a “bolt catch,” holds the bolt in a rearwards position, as discussed below. Bolt stop devices for hand-held firearms are known in the art, especially in handgun and combat rifles. The purpose of the bolt stop device is to retain the principal members of the bolt or bolt carrier mechanism in a rearward position. Retaining the bolt or bolt carrier mechanism in this rearward position is desirable as a safety measure to allow unobstructed view of the chamber of a firearm, to provide access to the chamber area for cleaning or other maintenance, to signal to the operator that the magazine is empty, and to provide a means for rapid reloading. With respect to the last advantage, when the bolt group is held rearward upon discharge of the last round in a magazine, an operator may eject the empty magazine, insert a fresh one, and then press a button on the side of the firearm to release the bolt and resume firing rounds. The bolt stop and bolt release button save an operator time from having to rack the bolt back to load a new round, and is standard on almost all semi-automatic rifles.
Know bolt stops typically include a bolt stop release button located on one side of the firearm. The Smith & Wesson model M&P 15 , for example, has a bolt stop having a bolt stop release button located on the left side of the firearm. In this and similar firearms, the bolt stop is a pivoted part on the outside of the lower receiver and is spring biased at the bottom of the part by a plunger and a spring in the receiver. The bolt stop further has a projection that stops the rotation of the bolt stop at the rear of the magazine well of the lower receiver. This projection is also contacted by the magazine follower once the magazine box is empty of rounds. As alluded to above, the magazine spring overcomes the bolt stop spring and plunger and rotates the bolt stop upward high enough to stop the forward motion of the bolt and hold the bolt in the open position. Pushing on the bolt stop release button of the bolt stop releases the bolt to chamber a round.
For the right-handed shooter, the bolt stop release button is easily accessible, for example, with a shooter's thumb or index finger. For a left handed shooter, however, the bolt stop release button is generally not accessible without a shooter having to release his grip on the firearm. Such action may be inconvenient. Moreover, in combat situations, even right-handed shooters are sometimes forced to switch from his/her dominant shooting posture to take advantage of cover and concealment. A right-handed shooter may not be accustomed to releasing and replacing a magazine and depressing the bolt stop release button in this position, thereby costing a shooter valuable time.
An ambidextrous bolt stop would thus allow a shooter, regardless of whether he/she is right handed or left handed, and regardless of shooting posture, to quickly and easily activate the bolt stop release button to chamber a new round from either the left side or the right side of the firearm.